Risk linked to common genes

Common genes are now thought to be behind the genetic risk for autism, rather than spontaneous gene mutations.

That’s the finding of a new study in Sweden involving 3,000 people with and without autism. It is described as one of the largest studies of its kind to date.

Researchers found that around 52 per cent of the autism cases were linked to common gene variants. Meanwhile, spontaneous genetic mutations accounted for only 2.6 per cent of the cases.

The study plays down the role of environmental factors in the development of autism.

‘Many small risk factors in genes add up’

Kathryn Roeder, professor of statistics and computational biology at Carnegie Mellon University in Pennsylvania, who co-led the investigation, said: “From the study, we can see that genetics plays a role in the development of autism compared to environmental risk factors … many small risk factors add up, each pushing a person further out on the spectrum.”

Another co-lead investigator was Joseph Buxbaum, from Icahn School of Medicine in New York. He said: “Although each exerts just a tiny effect individually, these common variations in the genetic code add up to substantial impact, taken together.”

Researchers ‘should focus on roots of autism’

Roeder said researchers should focus on looking for clues for the roots of autism. They should pinpoint what is causing the condition, he said. Estimates now put the incidence of autism in the US at one in 68 children.

Thomas Lehner is chief of the Genomics Research Branch at the National Institute of Mental Health in Washington DC.

He spoke of the ground-breaking nature of this new research. He said: “This is a different kind of analysis than employed in previous studies. Data from genome-wide association studies was used to identify a genetic model instead of focusing just on pinpointing genetic risk factors.”

As Buxbaum explained, many people have been focusing on de novo (spontaneous) mutations in genes. Such mutations can, for instance, occur in the sperm of an older father.

He said: “While we find these mutations are also key contributors, it is important to know that there is underlying risk in the family genetic architecture itself.

“The family may have common variation that puts it at risk, but if there is also a de novo mutation on top of that, it could push an individual over the edge. So for many families, the interplay between common and spontaneous risk factors could be the underlying genetic architecture of the disorder.”